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The KDJ11-B CPU board (M8190) is the second-generation QBUS CPU card using the J-11 chip set of the PDP-11 (the first being the the KDJ11-A CPU). It is a quad-height board, and is used in the PDP-11/83 and PDP-11/84 systems.

Its principal improvement over the KDJ11-A is its support of the Private Memory Interconnect bus, a high-performance variant of the QBUS; it also supports the KTJ11-B UNIBUS adapter, a QBUS->UNIBUS adapter used in the PDP-11/84.

It also provides a built-in serial console, ROMs to contain diagnostic and bootstrap programs, and an EEPROM to contain configuration information.

Like the KDJ11-A, the -B also contains an 8K-byte write-through cache (set size 1, block size 1 16-bit word), protected by parity. The KDJ11-B additionally provides two sets of tag fields for each cache entry, so that the CPU and DMA from the QBUS can interact with the cache simultaneously. Cache control logic inspects DMA transfers and invalidates cache entries for memory words which are written to by a device.

Also like the KDJ11-A, it can also use the FPJ11 floating point accelerator chip to speed up the FP11 implementation in the J-11.

As far as is known, the various models of the KDJ11-B differ only in their speed (CPU and clock crystal) and whether or not they come with the FPJ11. DEC documentation refers to certain models being used in certain machines, but as far as is known, in fact any model will work in any machine.

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